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Principle of Flow Control Valve
- Actual example of flow control
- Our mechanical valves can be used for gas flow control in many ways. An example of the most popular method of constant flow control with a needle valve and flow controller is explained here.
(1) Flow control with needle valve
The needle valve controls the opening of a small orifice in a channel with a bar-shaped needle, controlling the flow by changing the channel resistance. The valve thus acts as a resistance.
The flow changes when the pressure applied to the valve changes. Therefore, a pressure regulator is provided in the preceding stage as shown in Fig. A to make the pressure applied to the valve constant, thereby
obtaining constant flow. This is an inexpensive method which is commonly used when the pressure loss on the valve outlet side does not change. Use a simplified type, precision type, or bellows type needle valve according to the usage.
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The flow changes when the pressure applied to the valve changes. Therefore, a pressure regulator is provided in the preceding stage as shown in Fig. A to make the pressure applied to the valve constant, thereby
obtaining constant flow. This is an inexpensive method which is commonly used when the pressure loss on the valve outlet side does not change. Use a simplified type, precision type, or bellows type needle valve according to the usage.
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(2) Flow control with variable primary pressure type flow controller
The variable primary pressure (supply pressure) type flow controller is made by combining the needle valve (1) and a pressure regulator.
It can keep the flow constant even if the primary-side pressure changes.
(Fig. B).
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It can keep the flow constant even if the primary-side pressure changes.
(Fig. B).
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(3) Flow control with variable secondary pressure type flow controller
In methods (1) and (2), the flow will change if the pressure loss of a load in the subsequent stage is large.
In that case, a variable secondary pressure (outlet-side pressure: load pressure) type flow controller is used to control flow according to the flow sheet shown in Fig. C.
This flow sheet is complete with respect to pressure change, and is used basically for our gas mixing equipment. The primary-side pressure is controlled by a regulator, and the flow controller immune to pressure changes on the secondary side enables flow control free of the influence of the primary and secondary pressure.
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In that case, a variable secondary pressure (outlet-side pressure: load pressure) type flow controller is used to control flow according to the flow sheet shown in Fig. C.
This flow sheet is complete with respect to pressure change, and is used basically for our gas mixing equipment. The primary-side pressure is controlled by a regulator, and the flow controller immune to pressure changes on the secondary side enables flow control free of the influence of the primary and secondary pressure.
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